Sorry it took so long to get you a response. Sometimes the weekends are slow.
Well, I have looked at what you stated and made a test form with Forms 6i. I think what I would do is add a radio button in your radio group that is for the purpose of the initial state. I would then change the property of the element to non-visible.
This will create the scenario you want I think.
Although, I couldn't find away around the no initial value problem for the radio group.